Method for depositing nitride film using chemical vapor deposition apparatus of single chamber type

ABSTRACT

The present invention relates to a method for depositing a nitride film using a chemical vapor deposition apparatus of single chamber type, and more particularly to a method for depositing a nitride film that is capable of depositing the nitride film in which an area of the nitride film at the top of an interlayer isolation film has a larger thickness compared to each area thereof at the sides and the bottom of the interlayer isolation film and/or a contact hole by regulating a mixture ratio of an ammonia gas and a silane gas, both of which being process gases, using a chemical vapor deposition apparatus of single chamber type.

TECHNICAL FIELD

The present invention relates to a method for depositing a nitride filmusing a chemical vapor deposition apparatus of single chamber type, andmore particularly to a method for depositing a nitride film that iscapable of depositing the nitride film with a different thickness foreach region of the nitride film using one chemical vapor depositionapparatus of single chamber type.

BACKGROUND ART

Generally, a semiconductor device is completed by forming variouspattern regions, such as a device separation film, an interlayerisolation film, an electric conduction film, a contact, etc. on asurface of a semiconductor substrate. The interlayer isolation film isformed of a silicon oxidation film or a nitride film (SixNy) such as aPSG (Phosphorus Silicon Glass), a BPSG (Boron Phosphorus Silicon Glass),an USG (Undoped Silicon Glass), etc. Here, the nitride film serves as aninterlayer isolation film. In addition, the nitride film may be used asan etching stopper film in an etching process, a barrier film forpreventing any damage of a lower film in a chemical mechanical polishing(CMP) process, a barrier film in formation of a minute pattern such as aself-aligned contact, or a material film for performing a variety offunctions, such as an oxygen diffusion prevention film for preventingany diffusion of oxygen into a semiconductor substrate in a deviceseparation process.

Moreover, in manufacturing a DRAM (Dynamic Random Access Memory) devicewith a property of data volatility, a metal being a low resistancematerial is used as material of word and bit lines to comply a minutepatterning trend due to a reduced design rule and to further improveread/write rates for data, instead of a conventional tungsten silicideor a doped silicon. To prevent heavy metal contamination and thermaltransformation of a metal material, which are caused by such a change,it is subject to a low thermal bundle process. Even in this process, thenitride film is used as a barrier film.

Such a nitride film is generally deposited by a thermal CVD (chemicalvapor deposition) process using a CVD apparatus of furnace type or by aPECVD (Plasma enhanced CVD) process using a plasma enhanced CVDapparatus of single chamber type.

At this time, In case of forming the nitride film using the thermal CVDapparatus, there is an advantage in that a loading effect and a surfaceroughness characteristic are excellent, resulting in a good stepcoverage, whereas there is a drawback in that a thermal bundle isgenerated in a wafer due to a long time exposure of the wafer to a hightemperature, resulting in a degraded electric characteristic due to adeterioration of an electric characteristic and a metal electrode of adevice produced on the wafer.

On the contrary, in case of depositing a nitride film using the plasmaenhanced CVD apparatus, there is an advantage in that since the nitridefilm is formed under a low temperature atmosphere, a generation of thethermal bundle can be minimized, whereas there is a drawback in that itis impossible to deposit the nitride film when a step is formed becausea loading effect and a step coverage characteristic are not good, and aquality of the nitride film is degraded compared to the thermal CVDprocess due to an existence of the plasma.

Meanwhile, in forming a small contact of a large scale ingegrationsemiconductor device with a pattern size 0.5 μm or less, when a blanketetching process using a plasma, and the like is to be performed after aspacer is deposited, it needs a profile of a nitride film 1 with anupper region of a larger thickness compared to thickness B of the sideregions or thickness C of the lower region, as shown in FIG. 1.

In this case, in the prior art, a first nitride film 2 a with anentirely uniform thickness as shown in FIG. 2 a is deposited using thethermal CVD apparatus having an excellent step coverage. Thereafter, asecond thick nitride film 2 b is deposited on a surface of the firstnitride film 2 a as shown in FIG. 2 b by moving the wafer into theplasma enhanced CVD apparatus such that a profile is obtained in which athickness of the upper region of the nitride film is larger compared tothat of each of the side regions and the lower region.

Thus, in the prior art, there exists a problem that it has complicatedprocesses because, in order to form the nitride film with a largerthickness at the upper region thereof compared to those of the sideregions and under region, the nitride film must be formed with a uniformthickness on the entire surface of the wafer using, as a first CVDapparatus, a thermal CVD apparatus with an excellent step coveragecharacteristic, and then must be, in a further process, formed with alarger thickness at the upper region using, as a second CVD apparatus,another CVD apparatus (i.e., a plasma enhanced CVD apparatus with a highinstallation at a top region).

There is another problem that when the wafer, in which a thermal bundleis generated due to the thermal CVD process in high temperature, ismoved from the thermal CVD apparatus to the plasma enhanced CVDapparatus, it is contaminated by impurities in air.

Accordingly, in the technical field of the present invention, there is aneed for a method for depositing a nitride film with a differentthickness for each region thereof in one CVD apparatus while furthersimplifying the process.

DISCLOSURE OF INVENTION

The present invention has been made to enhance the aforementionedproblems, and it is an object of the present invention to provide amethod for depositing a nitride film with a different thickness for eachregion using one CVD apparatus.

It is another object of the present invention to provide a method fordepositing a nitride film that is capable of depositing a nitride filmwith a greater thickness at the upper region thereof compared to thoseof the side regions or the lower region.

It is yet another object of the present invention to provide a methodfor depositing a nitride film with a different thickness for each regionwhile minimizing a generation of a thermal bundle and simplifying aprocess.

In accordance with one aspect of the present invention, the above andother objects can be accomplished by the provision of a method fordepositing a nitride film using a chemical vapor deposition apparatus ofsingle chamber type comprising a process chamber comprising a inlet gasline through which process gases are introduced; a shower head forspraying the introduced process gases; a heater on which a wafer isplaced; and a vacuum port for discharging the process gases, the methodincluding: a first deposition step of depositing a first nitride film byperforming a first nitride film deposition process while a mixture ratioof the ammonia (NH₃) gas and the silane (SiH₄) gas, which are theprocess gases, injected in order to first deposit the nitride film ismaintained at 100:1 or more; and a second deposition step of depositinga second nitride film on a surface of the first nitride film in-situ bymaintaining the mixture ratio of the ammonia gas and the silane gas at100:1 or less in order to secondly deposit the nitride film, afterdepositing the first nitride film, such that the nitride film has ahigher thickness at the upper region of the nitride film compared tothose of the side regions and the lower region thereof.

It is desirable that the ammonia gas is maintained in the range betweenabout 50 and 3000 SCCM, and the silane gas is maintained in the rangebetween about 2 and 40 SCCM. Moreover, it is desirable that a pressurein the chamber is maintained in the range between 10 and 350 torr, and atemperature in the chamber is maintained in the range between 600 and800° C. And, it is desirable that a nitrogen (N₂) gas, which is a fuzzygas for diluting the silane and ammonia gases, is maintained in therange between about 100 and 10000 SCCM.

In accordance with another aspect of the present invention, a mixtureratio of the ammonia (NH₃) gas and the silane (SiH₄) gas, which are theprocess gases injected in order to first deposit the nitride film, ismaintained in 5:1 or more to 50:1 or less, such that the nitride film isdeposited by single process with a larger thickness at the upper regionof the nitride film compared to those of the side regions and lowerregion thereof.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of thepresent invention will be more clearly understood from the followingdetailed description taken in conjunction with the accompanyingdrawings, in which:

FIGS. 1 to 2 b illustrate profiles of a nitride film deposited by aconventional method for nitride film deposition;

FIG. 3 is illustrates a CVD apparatus of single chamber type by which amethod for depositing a nitride film according to an embodiment of thepresent invention is performed;

FIG. 4 is a graph illustrating a tendency of a step coverage dependenton a mixture ratio of process gases injected for nitride filmdeposition;

FIGS. 5 to 7 illustrate step coverage characteristics of a nitride filmdependent on the mixture ratio of process gases as shown in FIG. 4; and

FIGS. 8 a to 8 e are cross-sectional views illustrating states of awafer on which a nitride film is deposited through a preferredembodiment according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

The present invention relates to an enhanced method for depositing anitride film which is capable of depositing the nitride film with adifferent deposition thickness for each region thereof by adjusting aratio of process gases in one CVD apparatus of single chamber type.Hereinafter, the present invention will be described in further detailby way of preferred embodiments thereof with reference to theaccompanying drawings.

FIG. 3 illustrates a CVD apparatus of single chamber type that isapplied to a method for depositing a nitride film according to anembodiment of the present invention.

Referring to FIG. 3, the CVD apparatus consists of a process chamber 10,an inlet gas line 12, a shower head 14 for spraying process gases, aceramic heater 16 on which a wafer is loaded, a heater support 18 forsupporting the heater 16, a vacuum port 20 for discharging the processgases, etc. The wafer 22 is loaded on the top of the heater 16 so that anitride film is deposited.

In the present invention, in forming the nitride film on a surface ofthe wafer using the CVD apparatus of single chamber type as describedabove, adjustment is done as to a mixture ratio of the process gasesthat are injected into the process chamber 10, such that the nitridefilm is deposited on the surface of the wafer 22 with a differentthickness for each region of the nitride film.

FIG. 4 is a graph showing tendency of a step coverage according to amixture ratio of the process gases injected to deposit the nitride film.

Referring to the graph, The X-axis indicates a mixture ratio of anammonia (NH₃) gas and a silane (SiH₄) gas, which are process gasesapplied to the nitride deposition, while the Y-axis indicates the stepcoverage tendency of the nitride film dependent on the mixture ratio ofthe process gases.

As seen from the graph, the step coverage characteristic is excellent,which represents a thickness ratio of the nitride film deposited onsides and top of a contact hole as the ratio of the ammonia in theprocess gases is relatively large, while the step coveragecharacteristic of the nitride film is degraded as the ratio of theammonia in the process gases is relatively small. That is, the nitridefilm is deposited with a similar thickness at each of the sides and topof the contact hole as the ammonia ratio is large, whereas the nitridefilm is deposited with a larger thickness at the top of the contact holecompared to those of the sides thereof as the ammonia ratio is small.

FIGS. 5 to 7 illustrate changes in a deposition thickness of the nitridefilm practically deposited on the wafer with the mixture ratio of theammonia and silane gases as shown in FIG. 4.

First, FIG. 5 is a view illustrating a deposited nitride film 30 when amixture ratio of the ammonia and the silane is about 2000:5 or more({circle around (1)} interval in FIG. 4). As seen from the Figure, thenitride film is deposited with a similar thickness at each of the sidesand top of the contact hole.

FIG. 6 is a view illustrating a deposited nitride film 40 when themixture ratio of the ammonia and the silane is about 500:20 or more toabout 2000:5 or less ({circle around (2)} interval in FIG. 4). As seenfrom the Figure, the nitride film is deposited with a greater thicknessat the top of the contact hole compared to those of the sides thereof.

FIG. 7 is a view illustrating a deposited nitride film 50 when theammonia and the silane are mixed with a mixture ratio of about 30:20 ormore to about 500:20 or less ({circle around (3)} interval in FIG. 4).As seen from the Figure, the thickness of the nitride film at the top ofthe contact hole is much greater compared to those of others, which maycause an over-hang.

The method for depositing the nitride film will be herein described inconnection with FIGS. 8 a to 8 e, which uses the fact that the thicknessfor each region of the nitride film is varied with the mixture ratio ofthe ammonia and the silane, which are the process gases. FIGS. 8 a to 8e are cross-sectional process views for explaining the method fordepositing the nitride film according to an embodiment of the presentinvention.

Referring first to FIG. 8 a, a landing pad 102 is formed on the surfaceof the semiconductor substrate 100 in which a transistor (not shown) hasbeen formed, and then a first interlayer isolation film 104 is coatedonto the entire surface of the substrate. Thereafter, a bit line 106made of a conductive material, such as a silicide, and a nitride filmmask 108 that functions as a hard mask with respect to the bit line 106are sequentially formed on the top of the semiconductor substrate 100 onwhich the landing pad 102 has been formed. Then, a nitride spacer 110 isformed at the sides of the bit line 106 and the nitride mask 108.

A second interlayer isolation film 112 is entirely formed on the top ofthe resultant object formed as above, and a contact hole 114 is formedthrough a typical etching process so that the surface of the landing pad102 is exposed (refer to FIG. 8 b).

Thereafter, through the processes as shown in FIGS. 8 c and 8 d, thefirst and second nitride films are deposited so that a nitride film,which is adapted to function as an etch barrier film, is deposited onthe entire surface of the semiconductor substrate 110 in which thecontact hole 114 has been formed.

At this time, in performing the nitride film deposition process, theammonia (NH₃) gas is maintained in the range between about 50 and about3000 SCCM (Standard Cubic Centimeter per Minute), and the silane gas(SiH₄) is maintained in the range between about 2 and about 40 SCCM.Also, the nitrogen (N₂) gas, which is used as a fuzzy gas for dilutingthe silane and ammonia gases, is maintained in the range between about100 and about 10000 SCCM, the process temperature is maintained in therange between about 600 and about 800° C., and the pressure in thechamber is maintained in the range between about 10 and about 350 torr.

Referring first to FIG. 8 c, there is shown a process for depositing thefirst nitride film 116 adapted to function as the etch barrier film. Thefirst nitride film 116 with an excellent step coverage characteristic isformed by depositing the first nitride film with a uniform thickness onthe surface of the semiconductor substrate 100, on which the contacthole 114 has been formed, through a mixture of the ammonia and thesilane at a ratio of about 100:1.

Subsequently, as shown in FIG. 8 d, in order to deposit the nitride filmwith a larger thickness only at the top of the second interlayerisolation film 112 in which the contact hole 114 has been formed, asecond nitride film process continues to be performed through in-situ inthe chamber with respect to the top of the semiconductor substrate 100on which the first nitride film 116 has been deposited.

That is, the second nitride film 118 is deposited so that the nitridefilm is formed with a greater thickness at the top of the secondinterlayer isolation film 112 compared to that of the area of thecontact hole 114 by maintaining the mixture ratio of the ammonia (NH₃)gas and the silane (SiH₄) gas to be 100:1 or less, while thesemiconductor substrate 100, on which the first nitride film 116 hasbeen deposited, is loaded on the heater 16.

Thus, if the nitride film is to be formed with a larger thickness at thetop of the second interlayer isolation film 112 compared to others, theprocess of two steps is applied for depositing the first and secondnitride films 116 and 118 using respective process gases mixed in themixture ratios of the ammonia gas and the silane gas being 100:1 or moreand 100:1 or less, respectively, as shown in FIGS. 8 c and 8 d.

The first and second nitride films 116 and 118 deposited through theprocess of two steps are differentially denoted by a dotted line asshown in FIG. 8 d.

Meanwhile, although not shown in the figure, in addition to the processof two steps as described above, the nitride film may be formed with agreater thickness at the top of the second interlayer isolation film 112compared to others, even with a single process for depositing thenitride film by maintaining the mixture ratio of the ammonia gas and thesilane gas to be 100:1 or less. In other words, it is possible to formthe nitride film with a greater thickness at the top of the secondinterlayer isolation film 112 compared to the area of the contact hole114 to be the structure as shown in FIG. 8 d even with the singleprocess.

After the top area of the second interlayer isolation film 112 is thusdeposited with the nitride film of the greater thickness as compared tothe area of the contact hole 114, the contact portion (i.e., a bottomportion of the contact hole 114) is opened through a dry etch so thatthe lower electrode 102 and the plug electrode 120 are electrically incontact to each other, as in the conventional deposition method.

After this process, the contact hole 114 is completely filled by coatinga conductive material onto the semiconductor substrate on which thenitride film has been deposited with a greater thickness at the top ofthe second interlayer isolation film 112 as shown in FIG. 8 e.Thereafter, a plug electrode 120 contiguous to a lower landing pad isformed by carrying out a planarization process, such as a chemicalmechanical polishing process or a blanket etching process. At this time,damage to the second interlayer isolation film 112 surrounding a bitline, upon the planarization process, can be prevented by the thicknitride film formed on the surface of the second interlayer isolationfilm.

Moreover, since the nitride film is deposited with a greater thicknessonly at the top of the second interlayer isolation film 112, it hasessentially no effect on the aspect ratio of the contact hole, therebyforming a complete plug without generating a void.

INDUSTRIAL APPLICABILITY

In the prior art, in case that a nitride film is to be formed with agreater thickness at the top of the second interlayer isolation filmcompared to others, the first nitride film is first deposited using athermal CVD apparatus having an excellent step coverage characteristic,and then the resultant substrate is moved into a plasma enhanced CVDapparatus to be subject to a process for depositing the second thicknitride film at the top of the second interlayer isolation film. Thus,there are problems that since the first nitride film is deposited andthen resultant substrate is moved into another CVD apparatus, processdelay and error rate increase arise and also two or more types of CVDapparatuses are needed.

However, in the present invention, the mixture ratio of the reactiongases is adjusted through one CVD apparatus of single chamber type. As aresult, after the first nitride film is formed, the second nitride filmcan be formed in-situ in the same CVD apparatus. Accordingly, error rateduring the wafer movement can be reduced and a separate CVD apparatus isnot required, thereby decreasing a work space.

As described above, the present invention has advantages in that it canbe carried out by simply adjusting a mixture ratio of the process gasesusing one chemical vapor deposition apparatus of single chamber type,and it is possible to manufacture a semiconductor device with aexcellent quality, in which steps of the process are simplified andproblems such as a thermal budget do not arise. Here, because onechemical vapor deposition apparatus of single chamber type is used,there is no need for a LPCVD process of high temperature, resulting in aminimized thermal budget.

What has been described is only descriptive of a method for depositingthe nitride film by way of the preferred embodiments of the presentinvention, and the present invention is not limited to the illustratedembodiments and may cover various modifications that may be occurred bythose skilled in the art, without departing from the scope and spirit ofthe invention as disclosed in the accompanying claims.

In other words, while the method for depositing a nitride film with adifferent thickness for each region thereof has been described by way ofthe process of forming the plug electrode contiguous to the landing pad,the present invention may be applied to other processes of making adifferent deposition thickness for each region.

1. A method for depositing a nitride film by chemical vapor depositionusing a chemical vapor deposition apparatus of single chamber typehaving a process chamber comprising a inlet gas line through whichprocess gases are introduced; a shower head for spraying the introducedprocess gases; a heater on which a wafer is placed; and a vacuum portfor discharging the process gases, the method comprising the steps insequence of: a first step of depositing a first nitride film on thelower, side and upper regions of a patterned trench formed on a wafer byperforming a first nitride film deposition process using a process gasat a first mixture ratio of ammonia (NH₃) gas and silane (SiH₄) gas, inthe range of 100:1 or more; and, a second step of depositing a secondnitride film on a surface of the first nitride film in-situ bymaintaining a process gas at a second mixture ratio of ammonia gas andsilane gas different from the first mixture ratio and in the range of100:1 or less in order to secondly deposit the nitride film, afterdepositing the first nitride film, wherein a pressure in the chamber ismaintained in the range between 10 and 350 torr, whereupon the first andsecond nitride films deposited together have a greater thickness at theupper region as compared to the side regions and the lower regionthereof.
 2. The method as set forth in claim 1, wherein the ammonia gasis introduced into the process chamber at a flow rate of between about50 and 10000 SCCM, and the silane gas is introduced into the processchamber at a flow rate of between about 2 and 40 SCCM.
 3. The method asset forth in claim 1, wherein a temperature in the chamber is maintainedin a range between 600 and 800° C.
 4. The method as set forth in claim1, including the step of introducing an inert gas into the processchamber at a flow rate between about 100 and 10000 SGGM to dilute thesilane and ammonia gases.
 5. The method as set forth in claim 4, whereinthe inert gas comprises nitrogen (N₂) gas.